The invention refers to a ply-bonding device for paper converting or similar machines, which includes a fixed support to which a movable unit is pivoted, said movable unit being provided with a pressure wheel which cooperates with a counter-roller, and a pressure means which forces said wheel against the counter-roller.
The wheel has knurled surfaces which cooperate with the smooth surface of the counter-roller (or vice-versa). A multiply paper web or similar material passes between the wheel and the counter-roller where the plies are bonded together by the high localized pressure between the protruding parts of the wheel and counter-roller. The wheel is urged against the counter-roller by a plenum chamber located between the fixed support and the pressure wheel bearing unit. The plenum chamber is inflated at a high pressure and pushes the wheel against the surface of the counter-roller. A number of ply-bonding units are disposed in side-by-side relationship along the axis of the counter-roller, each being provided with its own pressure wheel and all being urged by a single pressurized plenum chamber. The presence of a plurality of wheels, each provided with an independent movable unit hinged to the support structure, allows for spaced areas of ply-bonding on the multi-ply web between the pressure wheels and the counter-roller surface which may not be in a straight line because of flexural deformation of the counter-roller axis.
According to the prior devices, articulation between a stationary support and a movable unit is accomplished by a ball joint which, by ensuring more degrees of freedom, makes it possible to compensate for any lack of parallelism between the axis of the pressure wheel and the axis of the counter-roller.
Such mobility of the wheel-carrying unit with respect to the counter-roller is necessary, but it brings about a considerable problem inasmuch as the unit and the wheel may vibrate and also because paper particles tend to accumulate on said wheels. The vibrating mass is extremely large and the consequent dynamic loads on the counter-roller may lead to a rapid wear and to a damage of the wheel. This is a significant problem, especially when considering the high cost of such elements and, above all, the loss of production while the elements are being replaced.
The present invention provides a new ply-bonding group which, by ensuring individual adaptation of each wheel to the cylindrical surface of the counter-roller (even if the counter-roller is deformed), is able to drastically reduce the dynamic loads caused by vibration.
According to the invention, the pressure wheels are resiliently supported on the movable unit and the latter, under operating condition, has a pre-determined stationary position defined by a rigid abutment against the support to which it is hinged.
With this arrangement, the resiliency of the wheel support on the unit allows said wheel to conform to the cylindrical surface of the counter-roller, while the movable unit is rigidly supported and, therefore, does not enter into vibration. The resiliency of the wheel relative to its support on the unit allows its surface to adapt to the surface of the counter-roller, which may bend or flex under load. Thus the mass which vibrates is only the wheel mass (or a fraction thereof).
In a particularly advantageous embodiment of the invention, the wheel includes an outer cylindrical sleeve on which the knurled surface, cooperating with the counter-roller surface, is formed. Such outer cylindrical sleeve is, in turn, mounted on an inner resilient sleeve which is between the central core of the wheel and the outer sleeve. The inner resilient sleeve interposed between the knurled outer sleeve and the central core allows additional adaptation, and the mass, which may possibly vibrate, is, in this case, only that of the knurled outer cylindrical sleeve and, therefore, is even less than the mass of the whole wheel. The inner resilient sleeve may be made of rubber and, in this case, it provides an additional vibration-damping effect.
The wheel-carrying movable unit which, by this arrangement, is hinged to the support with only very limited movement (i.e., with only the possibility of rotating about an axis parallel to the axis of rotation of the wheel) also has a rigid extension carrying at its end a stop means arranged to contact a portion of the support of the unit.
The stop means may be suitably adjustable.
Under operating conditions, the wheel-carrying movable unit is pushed by the pressurized plenum chamber to a fixed position determined by cooperation between the stop means and the support. This forms a rigid mechanical system.
With the above and other objects in view, more information and a better understanding of the present invention may be achieved by reference to the following detailed description.